There are many devices which store or further process a supply of granular material in an industrial environment. Many devices, such as grain storage apparatus or pharmaceutical handling apparatus, are designed to simply direct a supply of granular material to containers for storage. Other devices, such as a variety of industrial fabricating devices, process the material to form a component therefrom. For example, a plastic injection molding machine typically accepts a supply of pelletized plastic material, melts the pellets, injects the resulting liquid plastic into a mold, and discharges a molded part after the part has formed and cooled.
The prior art with respect to devices which handle granular materials is best described by continuing the example with respect to a product-forming machine. In the past, it has been common to use an overhead hopper for feeding the granular pellets of raw material to the product-forming machines. A quantity of pellets is placed in a very large container, such as a self-contained feed hopper, positioned above and adjacent to the machine. This arrangement permits the pellets to be gravity fed continuously into the molding machine.
In this arrangement, all of the raw material in the overhead storage container is directed to the molding machine. Frequently, the supply of raw material includes unwanted microscopic foreign metal material or foreign metal bodies, in the form of metal fragments, screws, washers, or the like. Such unwanted metallic foreign contaminants are referred to as "tramp metals" in the industry. These contaminants may be found in the plastic materials as it comes from the manufacturer due to wear or flaws in the manufacturer's transportation, manufacturing, packaging or conveying machinery. Other metal contaminants may be introduced into the raw materials from operations associated with handling the material at the end manufacturing facility itself. In addition, the growing use of recycled plastic materials for molding purposes increases the frequency of contaminant occurrences in the raw material supplies. The process of reclaiming the recyclable plastics often results in unwanted metallic contaminants becoming intermixed with the recovered plastics as a result of poor separation techniques at material recycling facilities. Frequently, recycling houses process recyclable plastics by chopping them into pieces of suitable size for reuse in molding apparatus. These plastic pieces may contain minute metal contaminants, as well as imbedded metal brackets, screws, nuts, and so on.
The presence of these metallic contaminants in the raw materials being processed in product-forming machines is undesirable for a variety of reasons. Contaminants may actually damage an industrial machine or render the finished part unusable. Even if the part is properly formed, the customer may object to the presence of metal therein as it may cause unacceptable structural, visual, or magnetic aberrations in the finished part.
Magnetic separators have been installed at the feed side of such industrial processing equipment to insure that metallic contaminants are removed. A magnetic separator typically comprises a housing component which acts as an intermediate hopper adapted to be placed above the forming machinery for the infeed of raw materials. A plurality of magnets form a magnetic drawer adapted to be removably inserted and secured in place in the feed path of this housing. As the granular material feeds through the housing, the metallic particles are attracted to the magnets. Periodically, the drawer is removed and the metallic materials are physically cleared from the magnets. The drawer is then reinserted into the housing for additional service.
Existing separator systems typically seal the mating surfaces between the housing and the separator drawer with an open cell foam gasket. The punishing environment in which this equipment operates results in rapid deterioration of such gasket materials. This deterioration turns the gasket itself into a contaminant which may enter the housing, and ultimately, contaminates the material being processed.
Further, overhead hopper configurations have recently fallen out of favor because of the difficulties encountered in changing the overhead supply hopper when a change in raw material composition is needed. The hoppers are difficult to transport and manipulate since they may weigh several hundred pounds when loaded with raw material. To overcome these problems with overhead or gravity feed hopper systems, a vacuum-feed system has been developed to supply the raw granular material from a container disposed adjacent to the processing machine. Materials are drawn from the container by operation of a vacuum applied thereto and fed into the processing machine. Materials can be changed by merely redirecting the vacuum between supply containers at ground level.
In this new vacuum-feed environment, metallic foreign matter is quite easily drawn into the processing equipment with the raw material, making the use of a separator a virtual necessity. However, the open cell foam gaskets of conventional magnetic separators provide a very poor seal which prevents the machinery from operating properly in a vacuum fed manner.
Therefore, a need exists for a magnetic tramp metal separator for removing tramp metal from equipment utilizing non-metallic granular materials which resists deterioration during use and may be used with vacuum feed equipment. This need exists with respect to product-forming machines, granular handling equipment, and most other devices which handle granular materials.